Chronic hemodialysis patients report that sleep alterations are major sources of stress and problems adversely affecting the quality of their lives. Subjective analyses of the sleep-wake patterns of this group suggest that daytime sleepiness is a significant problem and daytime sleep is known to profoundly affect nighttime patterns. The purpose of this study is to describe the impact that hemodialysis and the time of day at which the treatment is given have on the sleep-wake cycle and to explore related effects on functional health status and quality of life. The sample will include 40 subjects: 30 hemodialysis subjects, 10 in each of three groups based on time of treatment, and a group of 10 matched control subjects with renal insufficiency not yet receiving hemodialysis. All subjects will be screened by one to two nights of laboratory-based polysomnography to eliminate those with significant primary sleep disorders. Those individuals meeting entrance criteria will then be monitored for two 48-hour periods in their natural environment via ambulatory polysomnographic equipment. Subjects will also complete quality of life and functional health status inventories. The data obtained from this study will provide a large, objective data base regarding the sleep-wake cycles of hemodialysis patients and the effects of these patterns on quality of life and functional health status. The study will determine if and the extent to which the time of day that the treatment is given affects day and nighttime sleep. The data obtained will also provide other information necessary to develop population-specific interventions designed to manage sleep alterations in the hemodialysis population.